It is known that, in blood clotting, the soluble fibrinogen is converted by thrombin into the insoluble fibrin. Plasmin, which is present in the blood as plasminogen (prestage) and is blocked by antiplasmins, serves to break down the fibrin coagulum again.
On this basis, for example, it has become possible in recent years to dissolve blood clots by the plasmin activator streptokinase with the help of the body's own plasmin. With this therapy both thromboses as well as cardial infarcts have been treated successfully. The streptokinase treatment, however, has not been widely employed because the mortality rate has been too high. This is because routine plasminogen determination has not hitherto been possible and, with rising plasmin activation, the danger of a hemorrhage increases.
Various methods and apparatus for measuring the plasminogen content are indeed already known, for example the Clot Lysis Time Recorder, manufactured by Medicon Limited, Glasgow, Scotland; the Enzo-Diffusion Fibrin-plate test of Hyland, Travenol International GmbH, Munich, and the plasminogen plate test of Behringwerke, Marbur, Lahn. These methods are unsuitable for routine purposes because, on the one hand, they are expensive and on the other hand they require too much time, i.e. they usually take between 6 and 48 hours. With nearly all methods for determining the plasminogen content of a sample, the dissolution of the coagulated fibrin is measured and this, however, is only accessible to measurement with difficulty. Inter alia, the length of time the known methods take to perform depends on the difficulty of separating the antiplasmins from the plasminogen, which hitherto has only been incompletely accomplished.